Verator front end

[Davor]

I had an impression that Verator is built around the Fisher concept of fixed X and Y channels that are in quadrature, and everything in between is achieved by X to Y injection by means of a 100k potentiometer. Most of the similar designs failed to observe that Fisher did in fact have a precise quadrature by means of sensing the Tx coil current. Everything other than perfect quadrature is certainly not better than the real thing.

[Verator]

I did not see Fisher as a prototype. Rather Whites5900 (6000) There is also squaring but done differently. What's the difference? The point is not the most quadrature, and the ability to influence it, then when needed. Especially in the low and very low frequency. 0 \ 90 do not need anytime, anywhere. It is a small subtlety Hirt instrument settings.General scheme of the auto-generators do not have sufficient solution. Even with the PLL. Here is the frequency of the movement of soil and target phase modulation in the receive path. Here this question all the spoils. I look for a solution from the point of view of an ideal approach. It is necessary to eliminate the phase flutter in the fixture. This is bad then work on weakly conductive targets

[Verator]

metal detector - a precision phase meter. If so, then the methods must be precision. Any where vibrations are not allowed.

[Davor]

... I look for a solution from the point of view of an ideal approach. It is necessary to eliminate the phase flutter in the fixture...

Very true, and the way to eliminate one of the sources of uncertainty (phase shifters) you can use exact 0/90° shift as produced directly in the oscillator.
To have a dead steady ground balance you need a precise 90° shift, and all adjustments shall be achieved from there. Real ground will be several degrees away from 90° unless you are beach hunting, but the very same ground balance is several tens of degrees away from 0°, and that's the way phase shifters with comparators do it. That's why a precise 90° is a real bonus. Variation of phase in Verator is achieved in phase adjust and discrimination adjust as you do anyway, so true 90° is only a bonus.

For reference see a Fisher 1225 schematic, and observe how the 90° reference is obtained by sensing a coil current via a 1ohm resistor. Just brilliant. You can have even more accurate 90° shift using flip-flops in the oscillator loop. And with dead accurate 50% duty cycle and less power consumption.

[Verator]

Verator is squaring of the crystal oscillator. Area independent of frequency, of the sensor. It is always the same. PLL \ Trigger will square the 0 \ 90 but the frequency of the generator will float, so why should it then? Especially at high frequencies. The receiver circuit frequency-dependent, non-linear. And vectors will change. This is not right.There is no question Verator with quadrature. It can select the desired degree. Phase TX always smooth and constant.The PLL circuit does not provide such precision as quartz. It's like in a conventional LC auto generator. Because no one does PLL Enough of the LC oscillator

[Verator]

Sometimes it is necessary to correct the phase of Y on -2-5 degrees for an adequate definition of weakly conductive. Make it possible to trigger the same quadrature RC elements. The comparator is working quite well.

Synchronizing the current loop is possible, but then the entire loop current flows through the cable connector, which is not good.

[Davor]

My point is that the tank locked oscillator is practically always on Tx frequency because it provides the very excitation of the coil. So it is not two oscillators of which one is a PLL chasing the other. No. It is ALWAYS on frequency, and only in few moments after switch on you may have + or - <90° deviation, not more. It is because every LC band pass filter can shift phase only + or - 90° and that's the beauty of this oscillator. Once it is locked, deviation will be less than 1°. At the same time the quartz oscillator, not being able to follow the tank resonance, will have much more deviation over the same terrain.

So in the end this tank locked loop solution IS more accurate than quartz, and quadrature extracted directly from it is surely better than from comparators.

BTW, you do not change phase at the comparators neither in Verator 4, nor Verator M. It is fixed at some predefined value near quadrature. I'm sure it will work better with real quadrature.

[Verator]

To argue that it is better to know what is. In Verator 4 no resonant circuit at all. Talking about the stability of the phase just is not necessary. It is always stable. Always! The current in the coil is always shifted by 90. It is an axiom. So working in Verator 4, it is not Verator 2-3 (M). Comparators are working as they work, and that is enough. Phase shift 0\90, and it can be shifted. This is not theory. So conceived and so works. 0 \ 90 is not always necessary. This is a mistake of the theory!RX input circuit your suggestion is good in itself for rezonant TX. For TX Verator 4 is not suitable spectr is too big and takes a lot of harmonics. That picture is that you have shown over the RX is not true. Simulated either unaware of the coil and stray capacitance of a strong resonance in the frequency range 20-40kHz

Never, under any environmental conditions current in the coil does not change the principle of 90. Nothing is not affected. The current value not may change the angle never in real TX No soil is not able to create one. Any resonant circuit will vary from lot. Anyone! In Verator 4 never.

[Davor]

OK, I understand that. However, your Rx is resonant, so all benefits of an aperiodic Tx are lost. From my point of view, you either go for both Tx and Rx resonant and they track each others changes because they both share the same environment, or, both Rx and Tx aperiodic and there is no tracking anywhere.

Anyway, my suggestion is that by using flip-flops quadrature in a loop of a tank locked loop you obtain 0/90° directly and accurately, so there is no need for the comparators. In principle you don't use the possibility of phase changing at the comparators (you do that at faze and disc controls), so I concluded that perfect quadrature would be beneficial. This could be very beneficial in a resonant Tx because it would always provide operation at perfect resonance (normal oscillators usually don't - they are mostly slightly off-resonance) and also have a perfect source of quadrature for switchers.
Apparently you are not interested to try it, and I think it is your loss.

[Verator]

PLL good decision. But Verator better. I do not use resonance to the receiver. I'm not that stupid. Soil that subtract.
The advantage of PLL is that the energy is 100% sine, square wave energy of the first harmonic is only 80%, and requires high power Transmit to compensate. For high frequencies does not fit, a maximum of 10-12kHz. This is not a theoretical scheme of the MD. It is practical.

[Verator]

I do not use emulators characteristics of resonant circuits. I use real instruments for measuring real resonances. That is depicted in Scheme means nothing. This is shown in principle. Need to decide for himself
Emulators show the theory. Not take into account some of the processes

[satdaveuk]

[ATTACH]24561[/ATTACH]These questions have already been raised many time ago. But were ignored.[ATTACH]24560[/ATTACH]

If we talk about the RX. and here it is impossible to apply the resonance! What's the point then? The receiving coil should have a linear phase. In general, the sensor must be linear phase.For a device with a phase notch (Tesoro, etc.) is irrelevant phase and amplitude stability. There it all is forgiven. But in the devices vector type Whites. phase stability is crucial. Not namely amplitude phase. Because the amplitude of the changes, both vectors XY. subtracting the same proportional change in the channel, these G. Phase deviation will change the ratio of the vectors and the inability to subtract the interference of the soil or in the channel G.You and I have a different understanding of the issue. For you to sample the instrument conditional Tesoro, for me, a different type, vector.Phase methods clippings / discrimination suffer interference. But there is worse than the accuracy of the detection, the soil is not deductible, it is ignored.In the vector method, the soil is subtracted. But there is a phase noise of ground which is much larger than the noise. He is very big! Especially when changing the sensor type. The approach to the issue should be integrated. And the reference phase TX fixed. Then, the receiving system must provide a linear signal reception target / soil. But if you go on the principle of resonance, it will not work. RX coil can not track the phase as well as the TX. They are completely different and are in different positions relative to the ground and the object. They have a different impedance.In systems such as sensors Whites Blue max. receiver line, no resonance.
Going back to the PLL would like to remind that in order to stabilize the loop tracking takes time. The loop can not operate in real time. She is always late. This is what raises questions about the influence of soil on the signal. Do not need it for the sake of noise and to compensate for the soil. This is the most important.
Any perturbation TX PLL will track it also is interference, as Sync all derives from the same PLL. The fact of the phase change of position is unacceptable. It can not move at all!

Hi Verator
Could you do me a favor by emailing me the Elektor 1981 tutorial in its entirety as I never managed to get that copy in English.
Would be very greatfull, My address is: [email protected]
Many thanks in advance

[Davor]

I managed to obtain a scanned copy, so here is the infamous excerpt in PDF. As such it is a fine example of fair use exempt in copyright lore.
Please note that the whole article is a kind of Elektor-ized advertisement of some sponsoring company that was there to obtain coils and other critical parts, and the article reeks on bad marketing turned science. You'll find some completely irrelevant bits exalted as a big breakthrough, so take caution.

[Davor]

Emulators show the theory. Not take into account some of the processes

On the contrary, once you understand what is going on in reality, simulators are there to lead you through to a better design, or to dispel some myths.
And you learn a lot.
And you can play with designs even in times your lab is not at hand, or under a lot of snow.

[Verator]

Myths certainly do not needHere's your emulator shows the phase and frequency response. But in fact, it does not correspond to what we have. Not shown is a resonance at 25 kHz for example. He is strong enough to influence.